Method of coating aluminum with lead



ilite Patented Aug. 21, 1962 This invention relates to immersion plating and more particularly to the immersion plating of aluminum with lead and lead base alloys.

Current trends in the manufacture of automobiles involve, Wherever possible and practicable, the substitution of aluminum and aluminum alloys for the much heavier ferrous metal. Considerable difficulty is involved in substituting aluminum or aluminum alloys for the ferrous metals of reciprocating mating parts such as aluminum liners and pistons because the mating surfaces of aluminum or aluminum alloys of the same or similar compositions, particularly under conditions of borderline lubrication as may be encountered in starting a cold engine, have poor compatibility. Under these circumstances, the mating reciprocating parts tend to seize and gall the stationary part so as to cause incipient Welding and metal transfer. These undesirable conditions may be eliminated or greatly minimized by coating one of the members With lead or a suitable lead base alloy.

It is an object of this invention to provide a simple immersion method for coating aluminum with lead and lead base alloys including lead-tin alloys, lead-antimony alloys, and lead-tin-copper alloys. It is a further obj ct of this invention to rovide immersion baths for use in plating these alloys onto aluminum or aluminum base alloys by a simple immersion process. Another object of this invention is to provide an aluminum or aluminum alloy piston coated With a metal selected from the class consisting of lead or lead base alloys.

These and other objects of the invention are accom plished by plating lead or lead alloys including lead-antimony alloys, lead-tin alloys, lead-tin-copper alloys and lead-tin-antimony alloys onto aluminum by simple immersion from an aqueous bath including an alkaline tartrate complex and gelatin, lead monoxide or acetate as the source of lead, potassium stannate as the source of tin, antimonyl potassium tartrate as the source of antimony and copper cyanide as the source of copper.

The following are preferred immersion bath solutions for use in plating lead and the various lead alloys indi- I cated.

Example I Lead monoxide 15.5 grams (0.0695 grammole).

Potassium hydroxide 8 grams (0.143 grammole).

Sodium potassium tartrate 102 grams (0.409 grammole).

Gelatin 7.5 grams.

Water Suflicient to make up one liter of solution.

The above solution plates out adherent, dense, finegrained deposits of substantially pure lead. Satisfactory lead coatings may be plated out from solutions in which the lead monoxide is varied from about to 16 grams (about 0.0670 to 0.0720 gram-mole), the potassium hydroxide from about 7 to 8.5 grams (about 0.125 to 0.152 gram-mole), the sodium potassium tartrate from about 95 to 110 grams (about 0.380 to 0.440 gram-mole) and the gelatin from about 5 to 10 grams. The potassium hydroxide may be replaced by a molecularly equivalent amount of sodium hydroxide if desired. The latter compound produces a somewhat coarser and darker deposit and potassium hydroxide is preferred for this reason.

Example 11 Lead monoxide 15 grams (0.0673 grammole).

Potassium hydroxide 7.9 grams (0.142 grammole).

Sodium potassium tartrate 105 grams (0.420 grammole).

Gelatin 7.5 grams.

Potassium stannate 1.75 grams (0.0067 grammole).

Water sufficient to make up one liter of solution.

The solution of Example II plates out by simple immersion an adherent, dense and fine-grained deposit of an alloy consisting of about 95% by Weight lead and 5% tin. Satisfactory lead-tin alloys may be plated from solutions in which the lead monoxide is varied from about 14.5 to 15.5 grams (about 0.0650 to 0.0675 gram-mole), the potassium hydroxide from about 7.5 to 8.2 grams (about 0.0134 to 0.0146 gram-mole), the sodium potassium tartrate from about to 120 grams (about 0.360 to 0.480 gram-mole), the gelatin from about 5 to 10 grams and the potassium stannate from about 1 to 5 grams (about 0.0038 to 0.0190 gram-mole). A variation of the potassium st-annate from about 1 to 5 grams will produce satisfactory lead-tin alloys ranging from about 0.5% to 10.0% by Weight tin and the balance substantially lead. In this bath, the potassium stannate serves as a source of tin. Sodium hydroxide may be used in place of the potassium hydroxide in molecularly equivalent amounts as in Example I.

Example III liter of solution.

The above composition is efiective in plating by simple immersion upon aluminum a dense, adherent, fine-grained deposit of a lead alloy consisting of about by Weight lead and 5% antimony. Satisfactory lead-antimony alloys may be plated on aluminum by simple immersion from a solution such as the above in which the lead monoxide is varied from about 14.5 to 15.5 grams. (about 0.0650 to 0.0675 gram-mole), the potassium hydroxide from about 7.5 to 8.5 grams (about 0.0134 to 0.0152

gram-mole), the sodium potassium tartrate from about 90 to grams (about 0.360 to 0.480 gram-mole), the gelatin from about 5 to 10 grams and the antimonyl potassium from about 1 to 5 grams (about 0.0031 to 0.0154 gram-mole). A variation in the antimonyl potassium tartrate of from 1 to 5 grams will produce satisfactory coatings of lead-antimony alloy ranging from 1.0% to 5.0% by Weight antimony and the balance lead. As in the previous examples, the potassium hydroxide may be replaced by sodium hydroxide in molecularly equivalent amounts if desired.

3 Example IV Lead monoxide 25 grams (0.112 grammole). Potassium hydroxide 5 grams (0.090 grammole). Gelatin 3 grams. Potassium stannate 4.2 grams (0.016 grammole). Sodium potassium tartrate 73 grams (0.292 grammole). Copper cyanide 13 grams (0.726 grammole). Potassium cyanide 9.5 grams (0.146 grammole). Water Sufficient to make up one liter of solution. The above composition is effective in plating by a simple immersion process a dense, adherent, fine-grained deposit of a lead alloy consisting substantially of about 6 5% by weight lead, 10% tin and 25% copper.

Example V Lead monoxide 26 grams (0.116 gram-mole). Potassium hydroxide 2.1 grams (0.0265 gram-mole). Gelatin 3 grams. Potassium stannate 2.1 grams (0.008 gram-mole). Sodium potassium tartrate 116 grams (0.464 gram-mole). Copper cyanide '17.8 grams (0.099 gram-mole). Potassium cyanide 19.5 grams(0.30 gram-mole). Water Sufficient to make up one liter of solution.

The above composition is eifective in plating onto aluminum by simple immersion a dense, fine-grained deposit of lead alloy consisting of about 63% by weight lead, 33% copper and 4% tin.

Satisfactory lead-tin-copper alloys may be plated onto aluminum by simple immersion from the above solutions of Examples IV and V in which the lead monoxide is varied from about to 30 grams (about 0.0670 to 0.135 gram-mole), the potassium hydroxide from about 5 to 10 grams (about 0.0893 to 0.178 gram-mole), the gelatin from about 3 to 5 grams, the potassium stannate from about 3 to 12 grams (about 0.0114 to 0.0456 grammole), the sodium potassium tartrate from about 50 to 120 grams (about 0.20 to 0.480 gram-mole), the copper (cuprous) cyanide from about 1 to grams (about 0.0056 to 0.11 0 gram-mole) and the potassium cyanide from about 8 to grams (about 0.123 to 0.460 grammole). Sodium hydroxide may be used in place of the potassium hydroxide as in the previous examples. These variations in the bath composition will produce coatings of lead-tin-copper ranging from 65% to 97% by weight lead. 3% to. 34% tin and 1% to 34% copper.

Example Vl Lead monoxide 22.3 grams (0.100 gram-mole). Potassium hydroxide 2 grams (0.0358 gram-mole). Gelatin 5 grams.

Potassium stannate 2.5 grams (0.0095 gram-mole) Sodium potassium tartrate 5.1 grams (0.204 gram-mole).

Copper cyanide, 5.1 grams (0.0284 gram-mole). Versene 2 grams (0.0061 gram-mole). Water Suflicient to make up one liter of solution.

The above composition is effective in plating by a simple immersion process a dense, adherent, fine-grained deposit of a lead alloy consisting substantially of about 85% by weight lead, 5% tin and 10% copper. This bath illustrates that ethylenediamine tetraacetic acid referred to herein as Versene may be employed as a replacement for potassium cyanide in the baths of this invention. It has been found that 1.5 to 6 grams of Versene will correspond approximately to the 8 to 30 grams of potassium cyanide in the baths of Examples IV and V.

As previously indicated, molecularly equivalent amounts of sodium hydroxide may be employed in place of the potassium hydroxide in the plating baths of this invention. Molecularly equivalent amounts of soluble lead acetate may also be substituted for the lead monoxide. Sodium and/or potassium tartrate may be substituted for the sodium potassium double salt. The source of copper may be in the form of copper sulfate or copper acetate. However, it is preferred not to use these compounds in connection with cyanide solutions because of the danger of hydrogen cyanide gas production.

The preferred operating temperature range for the baths described above is about F. to :140 F. Excessive gassing results at temperatures in excess of 140 F. with the result that blistering and exfoliation of the plate occurs. Below 120 F., the plate exhibits marked tendency toward coarseness and dark deposits. In general, it is desired to employ a temperature range of about 120 F. to F. for baths from which a relatively low copper content alloy is plated, the temperature range of 130 F. to F. is preferred for use in connection with plating of alloys of relatively high copper and tin content.

The addition of up to about 10 grams per liter of potassium fluoride to the baths of Examples IV, V and VI helps decrease pitting and gas evolution when copper-containing aluminum alloys are being coated. In some instances sodium versenate may be substituted for a portion of the potassium cyanide to complex the copper. By the term sodium versenate is meant the di-sodium salt of ethylenediaminetetracetic acid.

In the above Examples I through V], the lead, tin, antimony and copper compounds serve as sources of the respective metals involved. The sodium potassium tartrate serves as a complexing agent to reduce the activity of the depositing ions. The gelatin promotes the formation of the non-spongy and adherent plate. The gelatin is essential since without it, the lead or lead alloy deposit becomes spongy and non-adherent. The sodium or potassium hydroxide is added to produce a pH range suitable for the stability of the metal complexes in the bath and to promote a displacement reaction by removing any oxide from the aluminum surface being coated. A pH range from 12.5 to 13.5 has been found suitable for this purpose.

As heretofore stated, dense, adherent, fine-grained lead alloy deposits may be formed on aluminum articles from the aforementioned baths by a simple immersion displacement process. A suitable immersion process is as follows. First, the aluminum article, such as an aluminum piston, is thoroughly degreased to remove grease, adhering dirt, etc. Any conventional degreasing method is suitable for this purpose. Next, the aluminum piston is etched in an acid bath for a time Slll'fiCiGHt to remove surface oxides and to produce a slightly roughened surface. A suitable etching treatment consists of immersing the aluminum piston for 30 to 60 seconds in a solution maintained at F. to F. and consisting of 2.5 milliliters of concentrated hydrochloric acid, 80 grams of trichloroacetic acid and 250 milliliters of lactic acid dissolved in an amount of water suificient to make up one liter of solution. After the etching treatment, the aluminum part to be immersion coated is rinsed in cold water to remove the excess etching solution. Finally, the aluminum part is immersed in the plating solution for a time suflicient to plate a desired thickness of lead base alloy thereon.

In general, the above-described plating baths may be operated from about room temperature. (about 70 F.) to about 140 F. Operating temperatures of about 120 F. to 140 F. have been found to produce particularly desirable results. In general, the rate at which the lead alloy coating builds up in thickness on the aluminum part increases with temperature. Lead alloy coatings applied from plating bath temperatures of over about 140 F. tend to blister and peel. The time of immera sion will depend upon the thickness of the lead alloy coating desired. Thus, at room temperature a coating of about 0.00015 inch thick will deposit in about three minutes. A coating having a thickness of about 0.0004 inch will deposit in about 20 minutes. In general, the plating rate tends to slow down as the coating becomes thicker.

After the aluminum article has been held in the bath for a period of time to produce a coating of a desired thickness, the coated article is removed from the bath and immediately rinsed in cold water to remove excess caustic solution. Thereafter, it is rinsed in hot water to facilitate subsequent drying.

On a bench test designed for studying compatibility of various materials running together in reciprocating motion without lubrication, it has been found that the use of a lead immersion coating greatly improves the compatibility of the two parts. In this test a small sample of D132 aluminum alloy having a /3 inch X inch bearing surface reciprocates against a /2 inch wide fiat surface of a stationary part made from a wear-resistant aluminum alloy containing 19% silicon and 5% copper. The length of the stroke is about /2 inch and the stroke rate is about 1200 cycles per minute. At a load of 110 pounds per square inch on the /8 X /2 inch contact area, the two materials, when uncoated, seize and gall within the first few strokes. When immersion coatings of tin, cadmium or copper, or electrodeposits of chromium are applied, the samples will run for about three minutes oefore seizure occurs. However, with the immersion lead coating herein described, a sample has run with no lubrication for more than eight hours without seizing, scoring or galling.

By the term aluminum as used in this specification and the appended claims is meant pure aluminum as well as alloys in which the pure aluminum is present in amounts of about 80% by Weight or more.

While the present invention has been described by means of certain specific examples, it Will be understood that the scope of the invention is not to be limited thereby except as defined by the following claims.

I claim:

1. An immersion plating bath comprising an aqueous solution having an initial pH of between 12.5 and 13.5 and containing the following in the concentrations indicated: lead ion about 0.0670 to 0.0720 gram-mole per liter, hydroxyl ion about 0.125 to 0.152 gram-mole per liter, tartrate ion about 0.380 to 0.440 gram-mole per liter and gelatin about 5 to 10 grams per liter.

2. An immersion plating bath comprising an aqueous solution having an initial pH of between 12.5 and 13.5 and containing the following in the concentrations indicated: lead ion about 0.0650 to 0.0675 gram-mole per liter, hydroxyl ion about 0.0134 to 0.0146 gram-mole per liter, tartrate ion about 0.360 to 0.480 gram-mole per liter, stannate ion about 0.0038 to 0.0190 gram-mole per liter and gelatin about 5 to 10 grams per liter.

3. An immersion plating bath comprising an aqueous solution having an initial pH of between 12.5 and 13.5 and containing the following in the concentrations indicated: lead ion about 0.0650 to 0.0675 gram-mole per liter, hydroxyl ion about 0.0134 to 0.0152 gram-mole per liter, tartrate ion about 0.360 to 0.480 gram-mole per liter, antimonyl ion about 0.0031 to 0.0154 gram-mole per liter and gelatin 5 to 10 grams per liter.

4. An immersion plating bath comprising an aqueous solution having an initial pH of between 12.5 and 13.5 and containing the following in the concentrations indicated: lead ion about 0.0670 to 0.135 gram-mole per liter, hydroxyl ion about 0.0893 to 0.178 gram-mole per liter, tartrate ion about 0.20 to 0.480 gram-mole per liter, stannate ion about 0.0114 to 0.0456 gram-mole per liter, cuprocyanide ion about 0.0056 to 0.110 gram-mole per liter, cyanide ion about 0.123 to 0.460 gram-mole per liter and gelatin 5 to 10 grams per liter.

5. An immersion plating bath comprising an aqueous solution having an initial pH of between 12.5 and 13.5 and containing the following in the concentrations indicated: lead ion 0.0670 to 0.135 gram mole per liter, hydroxyl ion about 0.0893 to 0.178 gram-mole per liter, tartrate ion about 0.20 to 0.480 gram-mole per liter, stannate ion about 0.0114 to 0.0456 gram-mole per liter, cuprocyanide ion about 0.0056 to 0.110 gram-mole per liter, Versene about 1.5 to 6 grams per liter and gelatin 5 to 10 grams per liter.

6. An immersion process for depositing lead and lead base alloys onto an aluminum body comprising the steps of immersing the aluminum body to be plated in a bath maintained between about F. and F. having an initial pH of 12.5 to 13.5 and containing the following in the concentrations indicated: lead ion about 0.0670 to 0.0720 gram-mole per liter, hydroxyl ion about 0.125 to 0.152 gram-mole per liter, tartrate ion about 0.380 to 0.440 gram-mole per liter and gelatin about 5 to 10 grams per liter.

7. An immersion process for depositing lead and lead base alloys onto an aluminum body comprising the steps of immersing the aluminum body to be plated in a bath maintained between about 120 F. and 140 F. having an initial pH of 12.5 to 13.5 and containing the following in the concentrations indicated: lead ion about 0.0650 to 0.0675 gram-mole per liter, hydroxyl ion about 0.0134 to 0.0146 gram-mole per liter, tartrate ion about 0.360 to 0.480 gram-mole per liter, stannate ion about 0.0038 to 0.0190 gram-mole per liter and gelatin about 5 to 10 grams per liter.

8. An immersion process for depositing lead and lead base alloys onto an aluminum body comprising the steps of immersing the aluminum body to be plated in a bath maintained between about 120 F. and 140 F. having an initial pH of 12.5 to 13.5 and containing the following in the concentrations indicated: lead ion about 0.0650 to 0.0675 gram-mole per liter, hydroxyl ion about 0.0134 to 0.0152 gram-mole per liter, tartrate ion about 0.360 to 0.480 gram-mole per liter, antimonyl ion about 0.0031 to 0.0154 gram-mole per liter and gelatin 5 to 10 grams per liter.

9. An immersion process for depositing lead and lead base alloys onto an aluminum body comprising the steps of immersing the aluminum body to be plated in -a bath maintained between about 120 F. and 140 F. having an initial pH of 12.5 to 13.5 and containing the following in the concentrations indicated: lead ion about 0.0670 to 0.135 gram-mole per liter, hydroxyl ion about 0. 0893 to 0.178 gram-mole per liter, tartrate ion about 0.20 to 0.480 gram-mole per liter, stannate ion about 0.0114 to 0.045 6 gram-mole per liter, cuprocyanide ion about 0.005 6 to 0.110 gram-mole per liter, cyanide ion about 0.123 to 1(1.460 gram-mole per liter and gelatin 5 to 10 grams per ter.

10. An immersion process for depositing lead and lead base alloys onto an aluminum body comprising the steps of immersing the aluminum body to be plated in a bath maintained between about 120 F. and 140 F. having an initial pH of 12.5 to 13.5 and containing the following in the concentrations indicated: lead ion 0.0670 to 0.135 gram-mole per liter, hydroxyl ion about 0.0893 to 0.178 gram-mole per liter, tartrate ion about 0.20 to 0.480 gram-mole per liter, stannate ion about 0.0114 to 0.0456 gram-mole per liter, cuprocyanide ion about 0.0056 to 0.110 gram-mole per liter, ethylenediamine tetraacetic acid about 1.5 to 6 grams per liter and gelatin 5 to 10 grams per liter.

References Cited in the file of this patent UNITED STATES PATENTS 2,297,241 Perner Sept. 29, 1942 2,726,175 Kendall et al Dec. 6, 1955 FOREIGN PATENTS 540,397 Canada Apr. 30, 1957 

6. AN IMMERSION PROCESS FOR DEPOSITING LEAD AND LEAD BASE ALLOYS ONTO AN ALUMINUM BODY COMPRISING THE STEPS OF IMMERSING THE ALUMINUM BODY TO BE PLATED IN A BATH MAINTAINED BETWEEN ABOUT 120*F. AND 140*F. HAVING AN INITIAL PH OF 12.5 TO 13.5 AND CONTAINING THE FOLLOWING IN THE CONCENTRATIONS INDICATED: LEAD ION ABOUT 0.0670 TO 0.0720 GRAM-MOLE PER LITER, HYDROXYL ION ABOUT 0.125 TO 0.152 GRAM-MOLE PER LITER, TARTRATE ION ABOUT 0.380 TO 0.440 GRAM-MOLE PER LITER AND GELATIN ABOUT 5 TO 10 GRAMS PER LITER. 